Selection and characterization of a nickel-tolerant cell line from tobacco (Nicotiana tabacum cv. bright yellow-2) suspension culture

To investigate the cellular/molecular mechanisms of nickel (Ni) tolerance in high-biomass-producing plants, we selected a Ni-tolerant (NIT) cell line from tobacco ( Nicotiana tabacum L. cv. bright yellow-2) suspension culture. Examination of response to various abiotic stresses showed that the NIT cells acquired remarkable tolerance to excess Ni, Cu, and Al but not to the other stresses. That the NIT cells accumulated approximately 2 m M Ni under the 700 µ M Ni condition suggests that the NIT cells can hyperaccumulate Ni and possess internal detoxification mechanisms for Ni. Two different sizes of putative β- d -xylosidase were constitutively secreted by the NIT cells, and the NIT cells showed greater elongation than the wild-type (WT) cells. Oxalate, citrate, 2-oxoglutarate, and glutamate contents were constitutively two- or three-fold higher in the NIT cells than in the WT cells, and histidine content was increased by up to three-fold in the NIT cells exposed to 700 µ M Ni compared to those in the WT cells. Newport green DCF diacetate (NPG), a Ni-specific fluorescence indicator, enabled the visualization of the subcellular localization of Ni in both WT and NIT cells. The NPG fluorescence was localized mainly in the vacuoles regardless of the WT or NIT cells under excess Ni conditions. The transport of Ni-organic acids and/or Ni-histidine complex into the vacuoles might be an important mechanism contributing to the high Ni tolerance of and the hyperaccumulation of Ni by the NIT cells.